1. Field of the Invention
The present invention relates generally to an apparatus and method for connecting replacement core spray piping to the shroud of a boiling water reactor. More specifically, the invention relates to an apparatus and method for connecting core spray piping to a BWR shroud without having to weld or bolt the replacement piping to either the shroud or piping internal to the shroud.
2. Description of Related Art
Boiling water reactors include core spray piping to provide cooling water to the fuel in the event a highly unlikely casualty occurs resulting in a loss of core heat removal capability, such as a loss of coolant accident (LOCA). This core spray piping receives water pumped from a reservoir, such as a pressure suppression pool, and delivers it to the core. The piping from the reservoir enters the reactor vessel above the core shroud, via a safe end. The piping then goes into a tee that divides the flow into two pipes. Each of these two pipes then curve around the interior of the vessel and connect to a vertically oriented downcomer pipe section. The downcomer pipe section extends downward into the region between the core shroud and the reactor vessel. The downcomer pipe section then enters the core shroud through another safe end and terminates in another tee located near the top of the shroud. The tee located within the shroud divides the flow into two semicircular core spray spargers supported on the interior of the core shroud. Typically, there are two of these spray systems per reactor vessel, which serve four semicircular spray spargers in the shroud.
The piping in the core spray systems is stainless steel, typically 304 SS, that is welded at each connection point. These welded connections are susceptible to intergrantular stress corrosion cracking (IGSCC), which can result in cracks and subsequent leakage from the spray system pipes. In the BWR core spray system, the downcomer piping section, including that portion extending through the shroud, has been particularly prone to IGSCC. As a result various devices have been devised for repairing this portion of piping.
One such device, disclosed in U.S. Pat. No. 5,735,551 issued to Whitman et al., includes first and second L-shaped housings. The housings surround the faulty piping, and are bolted together. A first seal is mounted within each housing to seal the housings against the outer periphery of the downcomer piping. A second seal is mounted at an end of the each housing to seal each against the outer wall of the core shroud. The housing assembly is retained against the outer wall of the core shroud by a threaded rod extending through the shroud. The threaded rod reacts at one end against the housing assembly, and at the other end against a cap mounted on the inside of the shroud.
The above-described device has several drawbacks. First, the housings require a high degree of casting accuracy to ensure tight coupling around the core spray line piping elbow. Second, the device is extremely difficult to assemble in its intended use environment. The device is intended for effecting a repair to a pipe in the downcomer region between the reactor vessel and core shroud, while this region is full of water. The amount of assembly parts required and the fitting tolerances make this device nearly unworkable in an underwater environment. Third, the cap is mounted directly onto the core spray sparger. Thus, a portion of the reaction force from the threaded rod acts on the sparger and is also transmitted to the existing downcomer piping. This arrangement increases the likelihood of damage to the sparger piping within the shroud and the likelihood of further damage to the downcomer piping.
Another device, disclosed in U.S. Pat. No. 5,737,380 issued to Deaver et al., provides for the permanent repair of core spray piping by replacing damaged piping with new piping. The replacement downcomer piping includes articulating vertical pipe connectors. These articulating pipe connectors allow for quick and easy pipe coupling, and also provide for thermal expansion and contraction without undue stresses. This device also has drawbacks. First, the downcomer elbow portion is bolted to the shroud, thus this portion of piping remains subject to rotational stresses. Second, this device requires precision holes to be made in the shroud. Third, device is time consuming to implement in the underwater environment of the downcomer region.
Thus, there is a need to provide a device and method for providing the permanent repair of core spray piping, while alleviating the stresses in the piping connecting to the shroud. There is also a need to provide a device and method for achieving this goal without undue cost, complexity, and time.
It is therefore an object of the present invention to provide an apparatus and method for connecting core spray piping to a BWR shroud without having to weld or bolt the replacement piping to either the shroud or piping internal to the shroud.
It is another object of the present invention to provide an inexpensive, quick, and easy-to-install apparatus and method for connecting core spray piping to a BWR shroud.
In one aspect of the present invention a shroud connection device for replacement core spray piping systems in a boiling water reactor comprises a pipe, a first coupling device, a second coupling device, and a rod. The pipe has a spherically shaped end and includes a penetration extending through it from an inside portion to an outside portion. The first coupling device has a first end dimensioned to receive the spherically shaped end and second ends, and a second end that abuts the outside portion of the shroud. The second coupling device has a third end that abuts the inside portion of the shroud, and a fourth end. The rod extends between the second coupling device and the penetration.
In another aspect of the present invention a device for connecting replacement core spray piping to a shroud in a boiling water reactor comprises flow directing means, interface means, force coupling means, and holding force transmitting means. The flow directing means directs core spray fluid flow within the reactor. The interface means receives an end of the flow directing means and transmits forces acting on the flow directing conduit to an outer wall of the shroud. The interface means completely surrounds a piping connection extending between inner and outer walls of the shroud. The coupling means provides a coupling force to couple the flow directing means to the interface means. The coupling force transmitting means transmits the coupling force to the inner wall of the shroud.
In yet another aspect of the present invention a method of connecting core spray piping to a shroud of a boiling water reactor includes an inserting step, two positioning steps, a connecting step, and an adjusting step. In the inserting step, a pipe having a spherically shaped end is inserted into a first end of a first coupling element. In the first positioning step, a second end of the first coupling element is positioned to completely surround at least a first end of a pipe connection extending through the shroud, and to abut an outside portion of the shroud. In the third positioning step, a third end of a second coupling element is positioned to completely surround a second end of the pipe connection, and to abut an inside portion of the shroud. In the connecting step, a tightening rod is connected between the second coupling element and a penetration extending from an inside portion of the pipe to an outside portion. In the adjusting step, the tightening rod is adjusted.
These and other objects, aspects, advantages and features of the present invention will become more apparent to those skilled in the art when the following detailed description is read in conjunction with the accompanying drawings.